[Bug c/71853] [6/7 regression] ICE on an ill-formed case statement in c_do_switch_warnings

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71853

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
That's because we're using uninitialized struct c_expr in
c_parser_switch_statement.  I have a fix.